About this report

This report publishes electricity risk curves (ERCs) against controlled storage over time. On 1 August 2019, the hydro risk curves (HRCs) changed to the ERCs and to include contingent storage in the presentation. The ERCs are published by the system operator and indicate the probability of energy shortage to the electricity system. These historical curves are available as presented to the market at the time.

Report notes

The system operator is responsible for publishing the electricity risk curves (ERCs) as part of its security of supply function. ERCs are produced for New Zealand and the South Island. Please see https://www.transpower.co.nz/system-operator/security-supply/electricity-risk-curves for current ERCs and further information. This responsibility for security of supply passed from the Electricity Commission to the system operator in November 2010.

The Authority undertakes industry and market monitoring, and shortage of hydro supply can impact things such as forward price expectations and market behaviours. This report tracks the history of the risk of shortage in the New Zealand electricity system, as reported by the system operator.

Hydro data (storage and/or inflows) is sourced from NZX hydro (data provided by NIWA) and is not available for download. Please see https://energy.nzx.com for more information.

On 29 August 2018 the system operator adjusted the treatment of Tekapo summer (denoted as 1 October – 31 March) contingent storage to be excluded from the HRC framework. This change removes 220 GWh from controlled storage over summer for NZ and the South Island. The change has brought the treatment of Tekapo contingent storage into line with the treatment of other contingent storage and the SoSFIP. In addition to small changes to the 2019 HRCs, the controlled storage, nominal full, and mean storage have all been adjusted. The mean storage we represent in the chart is no longer the mean of the data presented, but an adjusted mean to reflect the change from this point forward (i.e. without changing what was presented in the past). This treatment helps indicate to users that there is a sudden drop (1 October) or increase (31 March) in active controlled storage of 220 GWh.

The hydro risk curves are updated periodically including when there is a material change to the inputs. These updates are marked with a black triangle in the figure and have occurred for the following reasons:

06 Nov 2018: Updated generation outages for the next eight months that cannot be deferred in an emergency situation.

15 Nov 2018: Updated generation outages for the next eight months that cannot be deferred in an emergency situation and updated HVDC outages.

11 Dec 2018: Updated generation outages for the next eight months that cannot be deferred in an emergency situation and updated generator capacities.

31 Jan 2019: Updated generation outages for the next two months.

22 Feb 2019: Updated generation outages for the next two months and updated HVDC outages and updated demand forecast and included thermal generation derating due to gas constraints.

29 Mar 2019: Updated generation outages for the next two months and included thermal generation derating due to gas constraints.

30 Apr 2019: First publication of 2020 HRCs. The 2017 inflow sequence is now included in the HRC analysis. Updated generation outages for the next eight months, Ohaaki de-rating to 35MW from 40MW extended to June 2019, updated Whakamaru capacity from 112MW to 118 MW, 2020 HVDC planned outages included, and added the new Turitea wind farm (Mercury) modelled as 10MW in January 2020, with 10MW increases to capacity until reaching 120MW in December 2020.

21 May 2019: Updated generation outages for the next eight months, included 31.5MW of new Ngawha B generation from August 2020, updated Te Apiti capacity factors.

24 Jul 2019: Updated generation outages for the next eight months. Ohaaki capacity has returned to 40MW. Te Apiti capacity factor has returned to 0.342..

01 Aug 2019: Incorporated new Security of Supply Information and Forecasting Policy. Renamed from the Hydro Risk Curves (HRCs) to the Electricity Risk Curves (ERCs) that now include contingent storage in the methodology. Accompanied by three other sets of curves defining the contingent storage release boundaries, risk meter status boundaries, and OCC boundary triggers. This release also updates generation outages for the next eight months.